A conventional laminate sheet in which adhesive labels are laminated on a release sheet is shown in FIG. 13 (Japanese Utility Model Publication No. 6-18383, Japanese Patent Application Laid-open No. 8-316175). In recent years, it has become that such a laminate sheet 1P is used in the manufacture of an optical disk for laminating a cover sheet on a light-receiving surface of the optical disk. As shown in FIG. 13, the conventional laminate sheet 1P is constituted from a long release sheet 2P, and cover sheet portions 51P (adhesive sheets) provided in succession in the longitudinal direction of the release sheet 2P. Each of the cover sheet portions 51P comprises a pressure-sensitive adhesive layer 3P and an optically transparent base material 4P, and has the same shape as an optical disk.
The laminate sheet 1P is wound into a roll, and transported and stored in the form of the roll, and then is rolled out when used. In the case of winding the laminate sheet 1P into a roll in this way, a cover sheet portion 51P may have other cover sheet portions 51P rolled thereupon, whereupon the cover sheet portion 51P may be marked with the outlines (arc-shaped marks) of the other cover sheet portions 51P as shown in FIG. 14 due to the roll pressure.
To prevent the cover sheet portions 51P from being marked with arc-shaped marks as described above, one can envisage winding the laminate sheet 1P with a reduced roll pressure, but there is a problem that such a roll wound up with a reduced roll pressure is prone to collapsing.
Moreover, when winding the laminate sheet 1P, pieces of foreign matter such as minute pieces of dust (diameter generally 5 to 50 μm) may be trapped between sections of the laminate sheet 1P rolled up on one another. In the case that the laminate sheet 1P is wound up in this state with foreign matter trapped therein, depressions are formed in the cover sheet portions 51P due to the foreign matter.
In the case that such arc-shaped marks or depressions are formed on the cover sheet portions 51P, this has not been a great problem with conventional optical disks, but with a high-capacity/high-recording-density next-generation optical disk (Blu-ray Disc), such arc-shaped marks or depressions become defects, and errors in reading/writing data may arise due to these defects.
On the other hand, with a laminate sheet in which a long release sheet, an adhesive layer and a base material are laminated together, the laminate sheet may be wound into a roll, and transported and stored in the form of the roll, and then rolled out and punched into a desired shape to be used.
However, in the case that the laminate sheet is wound into such a roll, the laminate sheet is subjected to roll pressure, and hence the adhesive layer which is softer than other layers deforms over time due to the roll pressure, so that the smoothness of the surface of the adhesive layer is lost, and primarily due to this a so-called orange peel state results, whereby there is a problem of minute thickness irregularities arising in the adhesive layer. In the case that an adhesive sheet punched out from the laminate sheet is used, for example, as a cover sheet for the optical disk, then errors in reading/writing data to/from the obtained optical disk may arise due to the thickness irregularities in the adhesive layer.
Moreover, in the case that an adhesive layer that has undergone orange peeling is used, for example, for bonding an anti-reflection film for a display of a PDA (Personal Digital Assistant) or the like, there may be a problem of the transparency of the display being impaired, or the image sharpness decreasing.
To resolve the above problems, there have been proposed a laminate sheet in which a protective material thicker than the adhesive sheet is provided (Japanese Patent Application Laid-open No. 2004-35836), and a laminate sheet in which a protective material is provided on a base material at portions other than a main used portion of an adhesive layer (Japanese Patent Application Laid-open No. 2004-51914). According to each of these laminate sheets, when the laminate sheet is wound into a roll, the protective material acts as a spacer, and hence defects can be prevented from being formed on the adhesive sheet, and the smoothness of the surface of the adhesive layer can be maintained.